JPH06144047A - Four-wheel-drive type working vehicle - Google Patents

Abstract

PURPOSE:To secure a turning characteristic conformed to working conditions by constituting a car that it turns so sharply in a small radius at front-wheel speed increasing and rear-wheel one-side braking in time of selecting an automatic brake mode, and in time of the aforesaid releasing mode, it turns so as not to do damage to a surface of the ground at the front-wheel speed increasing alone. CONSTITUTION:Suppose an automatic brake mode is selected by the operation of a mode selector mechanism 50 and a steering operation on front wheels 1 is carried out by a steering mechanism 21 in this state intact, if so, a front-wheel gear shifter 7 comes to a state of being speeded up by each action of the cam mechanism 23 and both first and second linking mechanisms 25, 29, and simultaneously a side brake 27 of a rear wheel 2 at the turning center side is braked, and thereby the turning is performed in a small radius. If the front wheels 1 are steered by the mode selector mechanism 50 in a state that an automatic brake releasing mode is selected, the front- wheel gear shifter 7 is speeded up by the cam mechanism 23 and the first linking mechanism 25, but the side brake 27 will not work at all. In addition, at the time of high-speed running, the mode selector mechanism 50 is automatically turned to the automatic brake releasing mode by dint of energizing force of a checking mechanism 60, so that any small turn is obviated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front wheel shifting structure and a rear wheel braking structure when turning in a four-wheel drive type work vehicle.

[0002]

2. Description of the Related Art In a four-wheel drive type work vehicle as described above, as disclosed in, for example, Japanese Utility Model Laid-Open No. 1-107632, a standard state in which front wheels and rear wheels are driven at substantially equal speeds, In some transmissions, a front-wheel transmission that can be operated to switch to a speed-increasing state in which the front wheels are driven at a higher speed than the rear wheels is provided in a transmission system to the front wheels that can be steerably operated. This allows
When turning, the front wheel transmission can be switched to the speed increasing state to smoothly perform a small turn.

In this case, a pitman arm for the front wheels is provided with a cam mechanism, and the cam mechanism and the shift member of the front wheel transmission are mechanically interlocked and connected by a wire to set the front wheels from the straight ahead position to the right or left at a set angle. When the steering operation is performed as described above, the cam mechanism switches the front wheel transmission from the standard state to the speed increasing state.

[0004]

In an agricultural tractor, which is an example of a four-wheel drive type working vehicle, a pair of left and right side brakes that can independently brake the left and right rear wheels, and a pair of left and right side brakes for the side brakes. Equipped with a side brake pedal. Therefore, if the front wheels are accelerated by the front wheel transmission during turning and the side brake pedal on the turning center side is stepped on, a small turn can be made with a smaller radius. However, during such a turning operation, the side brake pedal on the turning center side must be depressed simultaneously with the steering operation of the front wheels by the steering handle, so there is room for improvement in terms of simplifying the turning operation.
Further, it is desirable that the small turn with the side brake applied to the braking operation is performed at a low speed. The present invention is configured such that turning using only the front wheel transmission and small-turn turning operation using the front wheel transmission and the rear wheel side brakes can be arbitrarily performed, and the front wheel shift can be performed only at an appropriate traveling speed. An object of the present invention is to make a small turn using a device and a rear wheel side brake, and to make the structure therefor highly durable.

[0005]

A feature of the present invention is that the four-wheel drive type working vehicle as described above is configured as follows. In other words, the front wheel transmission, which can be switched between the standard state in which the front wheels and the rear wheels are driven at substantially the same speed and the speed-up state in which the front wheels are driven at a higher speed than the rear wheels, is changed to the front wheels that are steerable. In order to prepare for the power transmission system, the cam mechanism provided in the steering mechanism for the front wheels and the front wheel transmission are mechanically interlocked by the first linkage mechanism, and the front wheels are set to the right or left from the straight traveling position by the steering mechanism. In a four-wheel drive work vehicle configured such that when the steering operation is performed at an angle or more, the front wheel transmission is switched from the standard state to the speed increasing state by the cam mechanism. The cam mechanism and the left and right side brakes are arranged so that the side brakes provided on the rear wheels on the turning center side are operated to the braking side in conjunction with the switching operation to the second state.
The operation lever of the mode switching mechanism is equipped with a mode switching mechanism that can be artificially switched between an automatic brake mode for interlocking and operating the second linkage mechanism by an interlocking mechanism and an automatic brake release mode for releasing the second interlocking mechanism. Can be held by an elastic detent mechanism in an ON position for providing the automatic brake mode and an OFF position for providing the automatic brake release mode, and the speed change mechanism for traveling is operated at a higher speed than the set speed. Then, there is provided a restraining mechanism for giving an elastic biasing force to the operation lever, which overcomes the detent mechanism and switches the operation lever of the mode switching mechanism in the ON position to the OFF position.

[0006]

According to the structure of the present invention, when the operation lever of the mode switching mechanism is in the ON position and the automatic brake mode is selected, the front wheel is steered by the steering mechanism from the straight ahead position to the right, for example, at a set angle or more. If you do
By the action of the cam mechanism and the first and second linkage mechanisms, the front wheel transmission is mechanically switched from the standard state to the speed increasing state, and the right side brake is also operated to the braking side. As a result, a small turn can be made with a small radius due to the speed-up action of the front wheels and the braking action on the rear wheels on the turning center side.

In a state where the operation lever of the mode switching mechanism is set to the OFF position and the automatic brake release mode is selected, when the front wheel is steered by the steering mechanism from the straight-ahead position to the set angle or more, the cam mechanism and the first mechanism are operated. By the action of the linkage mechanism, the front wheel transmission is mechanically switched from the standard state to the speed increasing state, but the side brake on the turning center side is not braked.

Further, when the traveling speed change mechanism is operated at a higher speed than the set speed while the mode switching mechanism is in the automatic brake mode, it is turned on by the urging force given by the check mechanism.
The operation lever at the position is switched to the OFF position to enter the automatic brake release mode, the cam mechanism is disconnected from the left and right side brakes, and the small turn is not performed. Also, when the traveling speed change mechanism is operated at a higher speed than the set value, the biasing force to the OFF position side that overcomes the detent mechanism is continuously applied to the operation lever, so the operation lever can be operated against the biasing force. However, when the operation lever is released, it is returned to the OFF position and cannot be held at the ON position. In other words, when traveling at high speed, a small turn does not appear due to the front wheel transmission and the rear wheel side brake being automatically operated.

[0009]

As described above, according to the present invention,
By switching the operation lever of the mode switching mechanism to the ON position and selecting the automatic braking mode, the operation of switching the front wheel transmission to the speed increasing state can be performed only by operating the steering wheel, and
Since the operation of the side brake on the turning center side to the braking side is automatically performed, it is not necessary to step on the side brake pedal at the time of turning, and the turning operation is simplified and the turning operability is improved. I was able to. In addition, by turning the operation lever of the mode switching mechanism to the OFF position and selecting the automatic brake release mode, it is possible to obtain a turning state only by increasing the speed of the front wheels, so that the vehicle makes a small turn without roughening the ground. It is now possible to select a turning mode having an arbitrary turning characteristic in accordance with the working conditions and the like, thereby improving workability. In addition, during high-speed traveling, small-turn turning using the front wheel transmission and the rear wheel side brakes was avoided in advance, so that forgetting operations or erroneous operations could not be performed, and handling was improved. . Moreover, the operating lever of the mode switching mechanism is turned on when traveling at high speed.
When trying to switch to the position, turn on the operation lever once
Since it can be operated, for example, when the means for locking the operation lever in the OFF position to prevent the occurrence of the automatic braking mode is restrained, the operation lever is forcibly turned ON to deform or damage the restraint mechanism. There is no fear and there is an advantage that it can be implemented with high durability.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an agricultural tractor will be described below with reference to the drawings. As shown in FIG. 14, an engine 3 is mounted on the front part of the machine body supported by the front wheels 1 and the rear wheels 2, and a mission case 4 is mounted on the rear part of the machine body to configure an agricultural tractor which is an example of a four-wheel drive work vehicle. is doing. Figure 1
Further, as shown in FIG. 15, the power from the engine 3 in the transmission case 4 is a main transmission mechanism M1 that performs a four-speed shift, a creep speed change mechanism (super speed reducer) M2 that allows high and low two speed shifts, and a forward and backward movement. Switching speed change mechanism M3, and
A traveling transmission including a sub-transmission mechanism M4 capable of high and low two-stage gear shifting is operated to be transmitted, and transmitted from the final transmission shaft 16 to the left and right rear wheels 2 via the rear wheel differential mechanism 5, and
The power branched from the final speed change shaft 16 is applied to the front wheel transmission 7,
Left and right front wheels 1 via front wheel transmission shaft 8 and front wheel differential mechanism 6
To be transmitted to.

Next, the front wheel transmission 7 will be described.
As shown in FIG. 13, the power is transmitted from the transmission gear 16a provided on the final transmission shaft 16 to the first standard gear 12, and the first standard gear 12 is transmitted.
The first speed increasing gear 13 through the standard gear 12 and the transmission shaft 11.
Have been transmitted to. A second standard gear 9 and a second speed increasing gear 10 are fitted on the front wheel transmission shaft 8 so as to be rotatable relative to each other, and the first and second standard gears 12, 9 and the first and second speed increasing gears 1 are provided.
Each of 3 and 10 is occluded.

The shift member 14 slidably fitted to the front wheel transmission shaft 8 and slidably attached to the second
When engaged with the standard gear 9, power is transmitted in a state where the front wheel 1 is driven at substantially the same speed as the rear wheel 2 (standard state). On the contrary, when the shift member 14 presses the multi-plate friction clutch 15 formed between the second speed-increasing gear 10 and the front wheel transmission shaft 8 and the clutch is turned on, the front wheel 1 is faster than the rear wheel 2. Power is transmitted while being driven by (acceleration state).

Next, the structure of the operation system of the shift member 14 of the front wheel transmission 7 will be described. As shown in FIG.
The shift fork 17 for the shift member 14 is externally fitted to the operation shaft 18 that is slidable in the axial direction via a spring 19 for accommodation, and the spring 20 having a weaker biasing force than the spring 19 causes the shift fork 17 to move. It is urged toward the side of engagement with the second standard gear 9 (standard state side). On the other hand, as shown in FIGS. 2 and 1, a pitman arm 22 for steering operation of the front wheels 1 is supported by the power steering mechanism 21, and a cam mechanism 23 composed of a cam plate is fixed to the pitman arm 22. And the pin 24a of the cam arm 24, which is swingably supported around the longitudinal axis P1 of the machine body fixing portion, is
3 is engaged with the cam hole 23a. Then, the first linking mechanism 25 made of a wire is connected across the distal end of the cam arm 24 and the operation shaft 18.

With the above structure, when the steering wheel 26 is operated and the power steering mechanism 21 swings the pitman arm 22 from the straight-ahead position to the right or left over the set angle, that is, the front wheel 1 is moved from the straight-ahead position. When the steering operation is performed to the right or left over the set angle, as shown in FIG. 3, the cam action of the cam hole 23a and the pin 24a causes the cam arm 24 to swing to the left in the drawing, and the first linkage. Mechanism 2
5 is pulled to the cam arm 24 side. This allows
The operation shaft 18 and the shift fork 17 of FIG. 13 are slid to the left in the figure, and the shift member 14 is moved to the friction clutch 1.
5 is pressed to turn on the clutch, and the front wheels 1 are driven to speed up.

As shown in FIG. 1, a pair of left and right side brakes 27 that can independently brake the left and right rear wheels 2 are provided. Next, the operation structure of the left and right side brakes 27 will be described. A pair of brake operating mechanisms 33 are provided for the pair of left and right side brakes 27. As shown in FIGS. 5 and 6, the brake operating mechanism 33 has
An L-shaped brake arm 28 is swingably supported around an axis P2, and the lower end of the brake arm 28 in the drawing and the side brake 27 are rod-shaped second linkage mechanisms 2.
9 are linked together. As shown in FIGS. 1 and 6, a pair of left and right side brake pedals 30 is provided on the right side of the control section of the aircraft, and as shown in FIGS. 1, 5 and 6, one end of the side brake pedal 30 and one end of the brake arm 28 are provided. Are linked and linked by a linking rod 31 and a connecting pin 32. With the above structure, for example, when the left side brake pedal 30 is depressed, the linkage rod 31 is pulled upward in the figure as shown in FIG. 7, the brake arm 28 swings counterclockwise in the figure, and 2 linkage mechanism 29
Thus, the left side brake 27 is operated to the braking side.

Next, the left and right side brakes 27 and the front wheel 1
The cooperation with the power steering mechanism 21 for vehicle will be described. As shown in FIGS. 5 and 6, the brake operating mechanism 3
The operation arm 34 is independently swingably supported with respect to the brake arm 28 around the axis P2 of the third arm 3, and the linkage arm 36 is provided around the support pin 35 at the tip of the operation arm 34.
Is swingably supported. As shown in FIG. 6, a torsion spring 37 for urging the linkage arm 36 in the clockwise direction in the figure is attached to the support pin 35, and a vertically long concave portion 36a is formed on the left side of the linkage arm 36 in the figure. Has been done. As a result, the connecting pin 32 of the brake arm 28 is inserted into the recess 36a of the linking arm 36 by the urging force of the torsion spring 37.

As shown in FIGS. 1, 2 and 4, a right operation arm 39 is swingably supported around a vertical axis P3 of a right frame 38 at the front of the machine body, and a right brake operation mechanism 33 is provided.
The support pin 35 of the operation arm 34 and the right operation arm 39 are interlockingly connected by the second linkage mechanism 41 including a spring 40 and a wire. Vertical axis P4 of the left frame 38
A support shaft 42 is rotatably supported around the left first operation arm 43 at the upper end of the support shaft 42, and a left second operation arm 44 at the lower end. Then, the support pin 35 of the operation arm 34 of the left brake operation mechanism 33
And the left second operation arm 44 are interlockingly connected by a second linkage mechanism 41 including a spring 40 and a wire. Stoppers 46 that stop the right operation arm 39 and the left second operation arm 44 in the postures shown in FIG. 2 are fixed to the left and right frames 38. Further, as shown in FIGS. 2 and 5, a spring 45 for urging the operation arm 34 in the clockwise direction in the drawing is attached to the support pin 35 of the operation arm 34 of the brake operation mechanism 33.

With the above structure, when the front wheel 1 is steered to the left over a set angle, the pitman arm 22 swings downward as shown in FIG.
Comes into contact with the left first operation arm 43, and the left first and second left operation arms 43 and 44 are rocked in the clockwise direction in the drawing.
As a result, the left second linkage mechanism 41 causes the left first and second left linkage mechanisms 41 to operate.
When the operation arms 43 and 44 are pulled, the operation arm 34 of the left brake operation mechanism 33 swings counterclockwise in the figure. In this case, since the connecting pin 32 of the brake arm 28 is inserted into the recess 36a of the linking arm 36 as shown in FIG. 3, when the linking arm 36 is pulled up in the drawing as the operation arm 34 swings, The brake arm 28 is also swung counterclockwise in the figure by the engagement between the recess 36a and the connecting pin 32, and the left side brake 27 is moved.
Is operated to the braking side.

As described above, when one of the side brakes 27 is operated to the braking side by the steering operation of the front wheels 1, the cam mechanism 23 and the cam arm 24 shown in FIG.
As the linkage mechanism 25 is pulled, the front wheel transmission 7 is switched from the standard state to the speed increasing state as described above. As described above, when the front wheels 1 are steered by the set angle or more, the front wheel transmission 7 is switched to the speed increasing state and the front wheels 1 are driven to speed up, and by the action of the right or left brake operating mechanism 33, The side brake 27 of the rear wheel 2 on the turning center side is operated to the braking side.

As shown in FIGS. 5 and 6, the link rod 31 on the side brake pedal 30 side is provided with a long hole 31a, and the connecting pin 32 is inserted into the long hole 31a. As a result, even if the front wheel 1 is steered over the set angle as described above and the operation arm 34 and the brake arm 28 swing counterclockwise in the figure as shown in FIG.
Only the connecting pin 32 moves upward in the drawing, but the side brake pedal 30 is not operated.

Further, when the side brake pedal 30 is depressed to move the link rod 31 upward in the figure in the state shown in FIG. 2 (the state in which the second link mechanism 41 is not pulled in the straight running state), As shown in FIG. 7, the brake arm 28 swings counterclockwise in the figure, and the connecting pin 32 only moves upward in the recess 36 a of the linking arm 36 in the figure, so that the operating arm 34 and the linking arm 36. Does not move in the posture shown in FIGS. 2 and 7.

When the front wheels 1 are steered by a set angle or more, the automatic brake mode in which the side brake 27 on the turning center side is automatically braked and the automatic brake release mode in which the brakes are not operated are set as described above. A mode switching mechanism 50 capable of switching to the above is provided, and the structure thereof will be described below. As shown in FIGS. 8 and 9, the T-shaped lever 51 is swingably supported around the horizontal axis P5 of the control section of the machine body, and the operation lever 52 extends from the center of the T-shaped lever 51. ing. As shown in FIGS. 1, 2, and 8, the linking arms 36 of the left and right brake operating mechanisms 33.
And a wire 53 is connected to each end of the T-shaped lever 51. Further, a pair of recesses d1 and d2 are formed in a predetermined phase on a boss portion 51a fixed to the center of the T-shaped lever 51, and a ball 55 biased by a spring 54 is provided in the recessed portion d1 and d2. ON the character lever 51 and the operation lever 52 to bring about the automatic brake mode
A detent mechanism 56 for positioning and holding the position and the OFF position for providing the automatic brake release mode is configured. The recess d1 at the ON position is set shallow and the recess d2 at the OFF position is set deep.

As shown in FIG. 8, a mode switching mechanism 50.
In the automatic braking mode in which the T-shaped lever 51 and the operating lever 52 are operated to the ON position, as shown in FIG. 2, the linkage arms 36 of the left and right brake operating mechanisms 33 are oscillated in the clockwise direction in the figure, Recess 3 of linking arm 36
The connecting pin 32 on the brake arm 28 side is inserted in 6a. In this state, for example, when the front wheel 1 is steered to the left by more than the set angle, the operation arm 34 of the left brake operation mechanism 33 swings counterclockwise in the figure as shown in FIG. The brake arm 28 is oscillated counterclockwise in the figure by the engagement of the connection pin 32 with the connecting pin 32, and the left side brake 27 is operated to the braking side. Although not shown, when the T-shaped lever 51 of the mode switching mechanism 50 is in the ON position, this is detected by a limit switch or the like, and the monitor lamp is turned on to activate the automatic braking mode. You can see it.

When the operation lever 52 and the T-shaped lever 51 of the mode switching mechanism 50 are operated to the OFF position,
When the pair of wires 53 is pulled, the linkage arms 36 of the left and right brake operating mechanisms 33 are shown as shown by the chain double-dashed line in FIG.
Is oscillated counterclockwise in the figure, the recess 36a of the linking arm 36 is separated from the connecting pin 32 on the brake arm 28 side to the right in the figure, and the automatic brake release mode is set. In this automatic brake release mode, for example, even if the front wheel 1 is steered to the left over a set angle or more, the left brake operating mechanism 33 is operated.
By simply swinging the operation arm 34 in the counterclockwise direction in the figure,
The brake arm 28 is not swung counterclockwise in the figure, and the left side brake 27 is not operated to the braking side.

The mode switching mechanism 50 is constructed so that the operator can arbitrarily switch it as described above and has a mutual restraint relationship with the traveling speed change operation means. The structure of the restraint mechanism 60 will be described below. Will be described with reference to FIGS. An auxiliary shift lever 61 for operating the auxiliary transmission mechanism M3 and a creep transmission lever 62 for operating the creep transmission mechanism M2 are provided on the left side of the control section.
And are arranged so that they can swing back and forth around a common horizontal axis P6,
Both levers 61, 62, an auxiliary gear shift operation shaft 63 and a creep gear shift operation shaft 64 projecting from the side surface of the transmission case 4 are interlockingly connected via link rods 65 and 66, respectively.

A check lever 67 is loosely fitted on an extension of the creep speed change operation shaft 64 so that the balance can swing.
The lower end of the check lever 67 and the sub-transmission lever 61 are pin-connected with each other through a link 68 with a certain long hole interchange 69, and the upper end of the check lever 67 and the creep speed change lever 62 are connected via a link 70. The pins are linked with each other with a fixed long hole interchange 71. Then, a tension spring 73 is stretched over an arm 67b provided on the boss portion 67a of the check lever 67 and a bracket 72 fixed to the vehicle body, so that the check lever 67 is urged to swing clockwise in the drawing. There is. Further, one end 74a of the check wire 74 is connected to an arm 67c provided on the boss portion 67a of the check lever 67, and the other end 74b of the check wire 74 is connected to the remaining free end of the T-shaped lever 51.

As shown in FIG. 10, when both the auxiliary speed change lever 61 and the creep speed change lever 62 are in the low speed (L), the check lever 67 is counterclockwise against the biasing force of the tension spring 73. It is swung, and the one end 74a of the restraint wire 74 is allowed to be pulled in, and the ball 55 of the detent mechanism 56 is engaged in the shallow recess d1 to allow the operation lever 52 to move.
Can be operated and held at the ON position.

Even if only the sub-transmission lever 61 is operated at a high speed (H) from the state of FIG. 10, the long hole interchange 71 on the side of the link link 70 does not allow the check lever 67 to swing clockwise in the figure. Therefore, the slack state of the restraint wire 74 is maintained, and
From the state of FIG. 10, even if only the creep speed change lever 62 is operated at high speed (H), the long hole interchange 69 on the link link 68 side is provided.
Does not allow the restraint lever 67 to swing clockwise in the figure, so that the restraint state of the restraint wire 74 is maintained.

Further, as shown in FIG. 12, the auxiliary transmission lever 6
1 and the creep speed change lever 62 are both operated at high speed (H), the upper and lower elongated hole interchanges 69 and 71 are both restrained by the check lever 67.
Is allowed to oscillate in the clockwise direction in the figure, and the check lever 67 is oscillated and urged in the clockwise direction in the figure by the urging force of the tension spring 73.
a is pulled upward.

At this time, when the mode switching mechanism 50 is switched to the automatic brake mode, that is, when the operation lever 52 is operated and held at the ON position, the T-shaped lever 51 is detented by the pulling operation of the check wire 74. The holding force of the mechanism 56 is overcome to rotate it clockwise in the figure, the operation lever 52 is forcibly switched to the OFF position, and the mode switching mechanism 50 enters the automatic brake release mode.

On the contrary, when the operating lever 52 is operated to the ON position while both the sub speed change lever 61 and the creep speed change lever 62 are operated at high speed (H), the check wire 74 pulls the tension spring as described above. While the operation lever 52 can be operated to the ON position against the tension spring 73 while being biased by the operation lever 52,
When the hand is released from, the operating lever 52 is returned to the OFF position by the urging force of the tension spring 73.

That is, the auxiliary shift lever 61 and the creep shift lever 62 are so constructed as to mutually prevent the automatic braking mode from appearing in a high-speed traveling state in which both are operated at high speed (H). is there.

It should be noted that reference numerals are given in the claims for convenience of comparison with the drawings, but the present invention is not limited to the structures of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a plan view showing a linkage configuration of a steering mechanism, a front wheel transmission, and left and right side brakes.

2A and 2B are a plan view and a side view showing a linked state of a steering mechanism and left and right brake operating mechanisms when going straight.

FIG. 3 is a plan view and a side view showing a linked state between the steering mechanism and the left and right brake operating mechanisms when the front wheels are steered to the left over a set angle.

4 is a rear view of the vicinity of the front wheel steering mechanism in FIG. 2 as viewed from the right side in FIG.

5 is a rear view of the vicinity of the brake operating mechanism in FIG. 2 as viewed from the right side in FIG.

FIG. 6 is a side view showing a configuration in which the left and right brake operating mechanisms are linked to the left and right side brakes and side brake pedals.

7 is a side view showing a state in which the side brake pedal is stepped on from the state shown in FIG.

FIG. 8 is a front view of a mode switching mechanism.

FIG. 9 is a cross-sectional plan view of a mode switching mechanism.

FIG. 10 is a front view showing a restraint release state of the restraint mechanism.

FIG. 11 is a partially cutaway plan view of the check mechanism.

FIG. 12 is a front view showing a check operation state of the check mechanism.

FIG. 13 is a vertical sectional side view of the front wheel transmission.

FIG. 14 is an overall side view of an agricultural tractor.

FIG. 15 is a block diagram of a transmission system.

[Explanation of symbols]

 1 Front Wheel 2 Rear Wheel 7 Front Wheel Transmission 21 Steering Mechanism 23 Cam Mechanism 25 First Linkage Mechanism 27 Side Brake 29,41 Second Linkage Mechanism 50 Mode Switching Mechanism 52 Operation Lever 56 Detent Mechanism 60 Checking Mechanism

Claims (1)

[Claims] 1. A standard state in which the front wheels (1) and the rear wheels (2) are driven at substantially equal speeds and a speed-up state in which the front wheels (1) are driven at a higher speed than the rear wheels (2). A front wheel transmission (7) that can be operated is provided in a transmission system to the front wheel (1) that can be steered, and a steering mechanism (21) for the front wheel (1) is provided with a cam mechanism (23) and the front wheel. Transmission (7)
And are mechanically interlocked by the first linkage mechanism (25),
When the steering mechanism (21) steers the front wheels (1) from the straight ahead position to the right or left over a set angle or more, the cam mechanism (23) causes the front wheel transmission (7) to shift from the standard state to the accelerated state. In a four-wheel drive type work vehicle configured to be switched, the front wheel transmission (7) is switched to a rear wheel (2) on the turning center side in conjunction with a switching operation from a standard state to a speed increasing state. The side mechanism (27) and the left and right side brakes (27) so that the provided side brake (27) is operated to the braking side.
And the second linkage mechanism (29) and (41) are interlocked and linked, and an automatic brake mode for linking and operating the second linkage mechanism (29) and (41) and an automatic brake release mode for releasing the linkage are manually operated. A mode switching mechanism (50) that can be selectively switched is provided, and an operation lever (52) of the mode switching mechanism (50) is elastically engaged between an ON position for providing an automatic brake mode and an OFF position for providing an automatic brake release mode. An operation lever (52) of the mode switching mechanism (50) which is configured to be held by a combined detent mechanism (56) and which is in the ON position when the traveling speed change mechanism is operated at a speed higher than the set speed. Of the operating lever (5) to overcome the detent mechanism (56) and switch it to the OFF position.
A four-wheel drive work vehicle equipped with a check mechanism (60) provided in 2).